This application claims priority under 35 U.S.C. xc2xa7119 to Swedish Application No. 9904617-9 filed on Dec. 16, 1999, which is hereby incorporated by reference in its entirety for all purposes.
1. Field of the Invention
The present invention generally relates to the field of antennas and particularly to a slot antenna device for transmitting and/or receiving radio frequency waves, and to a portable radio communication device including such a slot antenna device.
2. Description of the Related Art
In radio communication systems of today, there is an increasing demand for availability and small sized user terminals thereof. This puts high requirements on the antenna devices of these user terminals to be compact and to exhibit good antenna performance.
Antenna devices including a helical element in combination with an extendible whip antenna have been used for hand portable user terminals in order to achieve compact dimensions and durability, while still maintaining high radiation efficiency. Also, permanently protruding external antenna devices are used extensively.
Recently, attention has also been focused on antenna devices mounted inside the housing of hand portable terminals. Thereby, protruding antenna parts are avoided, lower radiation intensity towards the user may be obtained, and possibilities for further reductions of the size of the terminals are enabled, since many of these internal antenna devices may be achieved by means of thin film technology.
One solution includes a coaxial slot antenna installed in a radio communication device including an entire strip conductor arranged inside a flat conductive cubic, such that the strip conductor is insulated from the conductive cubic. The cubic is provided with a U-shaped slot crossing the strip conductor along the length thereof and in the height direction thereof. In one embodiment of this solution, a radio communication device has the coaxial slot antenna device embedded in a multilayer RF circuit board (PCB) mounted in parallel with and elevated from a base band terminal PCB. Further, the antenna RF PCB is provided with RF circuitry and additional circuitry. The antenna RF PCB and the terminal base band PCB are interconnected by a connector. The uppermost layer of this embodiment includes the coaxial slot antenna and RF circuitry laterally separated therefrom. A second layer is provided with power supply and control circuitry, and a third layer is connected to ground. A fourth layer is provided with intermediate frequency components, which are connected to base band circuitry arranged on the terminal base band PCB.
However, such an antenna structure of the above noted solution is not easily made very compact, operable in multiple bands or adaptively impedance matchable. Further, the structure is a rather complex, which due to required tolerances on the coupling with the feed, makes the structure difficult and expensive to manufacture. Also, the structure has no explicit shielding around the RF circuitry.
Additionally, when the terminals are manufactured to be smaller, the distances between various parts such as base band circuitry, RF circuitry, and radiating structures of the terminal become smaller, and thus electrical disturbances and interference between the various parts are increased. There is thus a need to provide a readily manufactured compact antenna device to be installed in a compact terminal, the antenna device reducing the amount of disturbances and interference in the terminal.
The present invention is therefore directed to an antenna device for a radio communication device which substantially overcomes one or more problems due to the limitations and disadvantages of the related art.
An object of the present invention is to provide an antenna device for a radio communication device, which exhibits an overall improved performance in comparison with antenna devices of the related art.
It is in this respect an object of the invention to provide an antenna device, which is easy and cheap to manufacture, easy to install and which enables an efficient use of the available space, and which exhibits good antenna performance.
Another object of the invention is to provide an antenna device, which is insensitive to conductive portions, such as e.g. a conductive radio communication device casing or the hand of a user, in the proximate environment of the antenna device.
It is a further object of the invention to provide an antenna device which when installed in a radio communication device exhibits, together with the radio communication device, reduced losses, e.g. due to resistivity in connection lines, as compared with radio communication devices of the related art.
It is yet a further object of the invention to provide an antenna device as an easily installable module including processing circuitry for RF signals.
It is a still further object of the invention to provide an antenna device that is small, lightweight and reliable, particularly mechanically durable.
It is an additional object of the invention to provide an antenna device suited to be used as an integral part of a radio communication device.
It is yet an additional object of the invention to provide an antenna device adapted for operation in at least two different frequency bands.
These objects among others are, according to the invention, attained by an antenna device that is connectable to a radio communication device including signal processing circuitry, the antenna device including a substantially planar conductive antenna element provided with a feeding point, a grounding point and a slot located between the feeding point and the grounding point; a substantially planar RF ground conductor generally located in a plane substantially parallel with the planar conductive antenna element; a grounding connector that connects the planar RF ground conductor to the grounding point; and a feeding connector that connects the signal processing circuitry to the feeding point, the antenna device being connectable to the radio communication device such that the planar ground conductor be located between the planar conductive antenna element and the signal processing circuitry to shield the signal processing circuitry from the transmitted and/or received RF waves.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.